Keyless entry and ignition systems are common in vehicles, and while they are a desirable convenience feature, they also increase the exposure of theft, given their inherent vulnerability to so-called man-in-the-middle or relay attacks. In such an attack, two persons (P1 and P2), each equipped with a computational device with a radio transmitter, collaborate to gain access to one or more vehicle operations, e.g., entry into, starting, and/or driving to thus enable one of the persons, e.g., P1, to steal a vehicle. For a relay attack, P2 moves within radio distance of a fob carried by the vehicle owner. P2's computational device relays signals between the fob and P1's computational device. P1's device relays signals between the vehicle and P2's device. This allows P1 to enter and start the vehicle, which is then typically driven to a garage specializing in re-keying of stolen vehicles. After gaining access to and starting a vehicle, there may be no further authentication between vehicle and the fob until the vehicle is again started or unlocked. While a continuously ongoing authentication between the vehicle and the fob would complicate the effort of P2 (to stay near the fob while P1 drives the vehicle), it would still not prevent theft.